Diabetic peripheral neuropathy (DPN) is increasingly common among older Americans, with a prevalence approaching 15%, and is a potent risk factor for falls. Previous work has shown that older persons with DPN have functionally significant impairments in lower extremity sensory and motor function that impacts postural control. An irregular surface, which challenges postural control, is a common source of falls in this population. Moreover, measures of gait variability on an irregular surface more effectively differentiate between older persons with DPN and those without, and between older persons with DPN who fall and those who do not, than similar measures on a smooth surface. We hypothesize that feedback loop delay in ankle joint force output in response to a perturbation, related primarily to a DPN-associated impairment in rate of strength generation, is the mechanism by which DPN leads to postural instability, which in turn results in increased gait variability and fall risk. Therefore the aims of this research are: 1) To measure feedback loop delay in ankle joint force output in a group of 40 subjects (30 DPN, stratified by severity, and 10 healthy old) and determine its ability to predict postural responses to discrete perturbations, provided by a novel shoe, under the medial and lateral forefoot using kinematic and force plate data; 2) To further evaluate the effect of feedback loop delay, utilizing the same subjects, by determining its ability to predict measures of gait variability on smooth and irregular surfaces; 3) To investigate the extent to which measures of gait variability, determined separately on smooth and irregular surfaces, predict the incidence of falls and fall-related injuries observed prospectively over one year in a group of 100 subjects with DPN. The resulting research will provide insights into the mechanism by which DPN impairs recovery from surface irregularities and identify the gait measure best able to predict falls and fall-related injuries in this high risk population. PUBLIC HEALTH RELEVANCE Walking as a form of exercise is a common and important treatment of adult onset diabetes mellitus. However, many older patients with diabetes have nerve damage in their feet and legs that causes them to fall, particularly when walking on irregular surfaces. This research will identify the reasons that such patients fall, and which patients are at greatest risk of falling and being injured. This information will lead to strategies for making such patient safer while walking.